Field of the Invention
The present invention relates to flowmeters that measure the flow rate of a liquid flowing inside a tube and to dialysis machines and medicinal solution injection devices that employ such a flowmeter.
Description of the Related Art
To date, various types of flowmeters that measure the flow rate of a liquid flowing inside a tube of a certain shape (hereafter, inside a tube) have been devised. Such a flowmeter is, for example, provided in a dialysis machine described in Patent Document 1 and is used in a case where, for example, the flow rate of blood is measured and control is performed so that the blood flows at a constant flow rate.
In Patent Document 2, a thermal-type flowmeter is described as an example of such a flowmeter that measures the flow rate of a liquid flowing inside a tube. In the flowmeter described in Patent Document 2, a plurality of thermally sensitive resistance wires are wound around an outer wall surface of a tube through which a liquid flows, the liquid being a target of flow rate measurement. The plurality of thermally sensitive resistance wires is wound at different positions from one another in the direction in which the liquid flows (upstream side and downstream side). A heater is mounted on the outer wall surface of the tube between the position at which the thermally sensitive resistance wire is arranged on the upstream side and the position at which the thermally sensitive resistance wire is arranged on the downstream side.
In the flowmeter described in Patent Document 2, the liquid inside the tube is heated by the heater. In the case where the liquid inside the tube is not flowing, the temperature sensed by the thermally sensitive resistance wire on the upstream side and temperature sensed by the thermally sensitive resistance wire on the downstream side are the same. In the case where the liquid is flowing inside the tube, the liquid heated by the heater flows toward the downstream side and therefore the temperature sensed by the thermally sensitive resistance wire on the downstream side is higher than the temperature sensed by the thermally sensitive resistance wire on the upstream side. Since the difference between the temperature sensed by the thermally sensitive resistance wire on the upstream side and the temperature sensed by the thermally sensitive resistance wire on the downstream side at this time is dependent upon the flow rate of the liquid flowing inside the tube, the flow rate is calculated in the flowmeter described in Patent Document 2 by detecting this difference in temperature.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 1-201263
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2-141621